The invention concerns panel shaped lightweight structural elements, containing internal reinforcing members, especially for constructing buildings and methods of constructing buildings composed of these elements.
At present various kinds of material are used in building construction. Most commonly used are stone, wood, bricks, concrete, metal, plast and similar materials.
Stone buildings are strong and mostly resistant to environmental deterioration, but their principal disadvantages are, that they are a limiting factor in architectural design, that they entail slow progress of construction work, are demanding in material handling efforts, entail costly transport, do not provide a sufficient thermal insulation, etc.
The application of wood as building material opens up more architectural design possibilities, it can easily be used in constructing roofs and floors. The main disadvantages of wood is limited strength, inflammability, shorter service life, limited insulation properties etc.
Brick buildings avoid some of the above mentioned problems. The main disadvantages of bricks are relatively slow progress in construction work, demands on accuracy of workmanship, higher costs in material transport and manipulation, the necessity to provide walls with surface layers etc. Bricks are joined together with mortar (grout), which also covers the gaps between individual bricks and can be used as surface layer of plaster or stucco. Plaster surface (rendering) can be applied to the indoor as well us to the outdoor wall surface. In earlier days brick buildings normally had wooden ceilings and floors, lately concrete has partly replaced wood in these applications.
Concretexe2x80x94or reinforced concretexe2x80x94constructions are remarkable for their strength, are sufficiently resilient to external influences, but their heat and sound insulation parameters are rather low, transport is rather demanding, on the building site heavy building mechanisms are unavoidable, up to now the problem of disposal with these buildings after their useful service life has expired, has no satisfactory solution etc. Floors are mostly constructed using beams, external surfaces are treated so as to resist to prevailing climatic conditions, indoor surface are rendered as the customer wishes.
Also, known are some less used kinds of natural materials for building construction: e.g. earth, reeds or rushes, bamboo, straw and similar. The use of these materials is limited to selected territories.
Also known are technologies based on the use of a combination of some of the above mentioned materials. This concerns e.g. wooden or steel basic constructions, where the free spaces are built up with bricks, concrete, wood, glass, plastic or other materials. The central filling may be made of thermo-insulating material, while the external surface layers are of wood, sheet metal, plywood, stucco and other materials. Internal surfaces can be of stucco, various linings, plasterboard etc. During the last decades wooden support structures are mostly being replaced by metal supporting structures, but the basic construction methods have not changed. Floors above ground level are usually of brickwork or of wood.
From the above it can be deduced, that there are two principle classes of building construction technologies: those that are assembled on the construction site of individual construction elements, like stone, wood, bricks etc., and those, which are assembled from prefabricates, transported to the erection site as subassemblies, mostly in the form of various panels.
Prefabricated subassemblies with iron or wooden internal support structures are manufactured in a production factory and transported to the construction site, where the building is assembled either entirely using these prefabricated panels and subassemblies, or partly of subassemblies and partly of components and elements assembled on the construction site.
Panels made of steel reinforced concrete have been widely used in the large scale construction of houses. Panels, with insulating and other surface layers or without them, are used to build complete houses, including floors, ceilings and roofs.
Further are known prefabricated panels using layered elements with a load carrying surface layer. These layered elements as a rule contain load carrying surface layers and between them one or two insulating or other fillers, as for example plywood, honeycomb structures etc. An example of a known arrangement is described in the patent number CA 1,284,571 of the year 1991, filed by Peter Kayne. There is a relatively large number of patents, which are based on this construction. The difference between these patents is in principle only in the materials used, possible in the arrangement or construction of the filler material. Some patents describe also the methods used for the production of these prefabricates, as well as the methods of joining individual layers to each other.
The patent number CA 1,169,625, filed by Jack Slater, concerns the panel itself and the method of building construction using this panel. The panel contains supporting studs of either metal or of wood, between which a polystyrene block is located. These panels can be used for making walls, but also floors. The studs are joined to the fillings by commonly known kinds of glue. The inner surface is usually covered with plaster board and the outer surface with bricks or other claddings. The finishing work on internal and external surfaces is in no way connected to the studs and thus cannot transfer any supporting forces, or forces acting outside the panels, besides their own gravity-related weight.
Another example of the presently known state of the art is to be found in patent CA 2,070,079 filed by Vittorio De Zen. This patent is based on forming hollow profiles of thermoplastic materials, which it is possible to assemble in various ways, possible to fill cavities with suitable material.
An inherent disadvantage of this solution is the high cost of the machinery (tool) needed for the pressing, difficult change of panels produced, more complicated assembly, lower mechanical strength, uneasy surface treatment etc.
In summary it can be said, that building construction using small elements is demanding in time, material, work force, transport etc. Construction based on prefabricated panels will overcome some of these insufficiencies, but are usually demanding on transportation, on-site machinery, qualified personnel etc.
The above described disadvantages are largely overcome by a lightweight structural element in the shape of a panel, especially for building construction, containing a support structure according to this invention. The lightweight construction element contains at least two supporting rods, which at their end are interconnected by cross-bars, between the supporting rods and the cross bars is a core and/or the surfaces of the supporting rods are interconnected by an adhesive structural skin made from material of thickness between 0.5 and 5 mm, of direct tensile strength from 5 to 35 MPa, tensile strength in bending from 5 to 45 MPa, modulus of elasticity from 2 to 30 GPa, specific density of the matrix material 1 to 2.7 g/cm3, the shear bond strength of the junction between the structural skin and the support rods is from 1 to 5 MPa and the compressive strength against pressure of the matrix material is from 10 to 70 MPa.
It is of advantage to make the lightweight structural element of at least two supporting rods of xe2x80x9cUxe2x80x9d profile, facing each other with their open side, possible of four rods of profile xe2x80x9cLxe2x80x9d, facing each other with their open side.
It is of advantage, to cover the core and/or the rods with a further layer from 5 to 50 mm thick, of direct tensile strength from 0.1 to 10 MPa, tensile strength in bending from 2 to 15 MPa, modulus of elasticity from 2 to 45 GPa, specific density of the matrix material from 1 to 2.7 g/cm3, the shear strength of the junction to the adhesive structural skin is from 0.1 to 5 MPa and the compressive strength against pressure of the matrix material is from 10 to 75 MPa. This further layer may contain plaster, cement, mineral fibres, perlite, vermikulite and other materials, with which desirable parameters can be attained as far as fire resistance, noise insulation etc. are concerned.
It is of advantage to make the core of polystyrene foam, extruded polystyrene, polyuretane foam, mineral wool, poro-cement, poro-silicates, honeycomb construction etc. The core can also be made of paper board, refuse material, earth, cellulose or mineral fibres.
It is of advantage to furnish an additional layer to the structural skin, with grooves for holding applied mortar.
Lightweight structural elements according to this invention can be used in such a way, that a layer identical to the structural skin material is applied to support posts and/or at least two neighbouring panels and it is of advantage to apply a further layer of this material two at least two neighbouring panels.
The advantage of this solution lies in the high value of strength of the lightweight structural element caused by the fact, that the entire lightweight structural element according to this invention behaves like one entity, because the support rods are between them firmly attached to the strong structural skin and therefore all internal and external stresses and loads are transferred to all the remaining components of this element. The ensuing constructionxe2x80x94the hollow panelxe2x80x94is capable of transferring high values of stress, from bending as well as from torsion loads, in horizontal as well as in vertical directions. Thus it is possible to exploit this lightweight structural element for walls as well as for floors, ceilings or roofs. In view of the fact, that the structural skin containing anti-corrosion inhibitors firmly adheres to the supporting rods, these are protected from corrosion. Thus it is possible to use also so called xe2x80x9cwetxe2x80x9d materials as fillers.
The lightweight structural element according to this invention can thus be used in its basic form, i.e. as a hollow panel, but also, and especially so, as a panel with a filler, which can be chosen to meet specific needs and available materials.
The filler improves the strength of the lightweight structural element, but at the same time, using suitably selected filler material, it can be possible to attain desirable properties for the whole element. This concerns for example fire resistance, heat and sound insulation, resistance to environment etc. Buildings erected using these elements will be advantageous in extremely hot regions, e.g. the Sahara, as well as in extremely cold regions, e.g. Antarctica. Under these extreme conditions it is of advantage to use rods of xe2x80x9cLxe2x80x9d profile. The basic construction element thus manages to transfer loads into all rods and into the entire surface layer of the element (structural skin).
Lightweight structural elements according to this patent are light, compact for storage, strong and therefore involved transport costs are low and during erection work no heavy machinery or special mechanisms or tools are needed. Basic tools and equipment for the erection site will suffice, e.g. a concrete mixer, pump etc. Erection workers need not be fully trained specialists, but can be only superficially trained. For construction work abroad it therefore is not necessary to send out specialists from the factory, but it is possible to use local workers, who have gone through a short training course. If it is found advantageous the filling can be made of material locally available in the region of the construction site.
The lightweight structural element itself, as well as the material used during the erection, are ecologically harmless and it is possibly to reuse them. The service life of the lightweight structural elements is comparable to presently used panels, possibly even longer. Their resistance to climatic impact, including strong wind and earthquake, is comparable to that of buildings erected using classical building material, possibly even greater.
A further advantage is the ease, with which exterior as well as interior surfaces can be adjusted to the customer""s desires. It is possible to finish the surfaces in a wide variety of ways, thus giving the final construction different features. These can make the building look anything from modest to luxurious, in any case it is not discernible, that the building has been made of prefabricates. Another advantage is, that the doors, windows etc. can be chosen from local suppliers. Furthermore the material is extremely resistant, fireproof, waterproof, possibly even water tight. A further advantage is, that it is possible to use the panels as substructure for poured floor mortar. This floor will be adequately strong with desired surface parameters.
A great advantage is the speed, with which the erection takes place. A complete house can be erected in 2 to 3 days with the aid of 3 to 4 workers.
A further advantage is the low price. This is caused by the fact, that the support rods are of xe2x80x9cUxe2x80x9d or xe2x80x9cLxe2x80x9d cross section. Previously known rods for reason of sufficient mechanical strength had to be of profile xe2x80x9cCxe2x80x9d, i.e. the open end needed an additional operation of rolling in. That entails high production costs. xe2x80x9cUxe2x80x9d or xe2x80x9cLxe2x80x9d profiles are cheap to manufacture and can even be pressed, which is cheaper and simpler than other fabrication operations. In view of the simple shape of the elements used there is no problem in changing the size of the end product according to momentary needs.